RP090 - Characterization and Use of Polyfluorosiloxanes in Automotive Applications, Motorola Inc., Anthony Polak
ABSTRACT
Polysiloxanes are routinely used in the semiconductor industry as die encapsulants. Thermal analysis, NMR, ion chromatography, and dielectric spectroscopy was used to characterize these polymers. The dielectric loss spectrum was found to be directly related to the long term electrical stability of the encapsulated die, and was also found to be a more sensitive technique for determining the concentration of electronically active impurities than GC/MS, and ion chromatography.
Dielectric spectroscopy was also used to study the diffusion of acids, and water through these polymers. While the solubility of acids and water in these materials is low, their diffusion constants are high, on the order of ten to the minus four sq.cm./s. In addition, the interaction of the encapsulant with the Si3N4 passivation used on the die surface was found to have an effect on the long term stability of the device. This is believed to be due to the formation of a conductive layer at the Si3N4/polymer interface which ultimately forms a leakage path between the bond pads, or into the Si3N4 passivation layer.
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